1. Technical Field
The invention relates to an ultrasonic device for the non-destructive testing of thin tubes, of the type comprising a head insertable in the tube and having centering means in the tube and means for imparting to the head a rectilinear motion along a longitudinal axis and a rotational motion about the axis.
The invention is particularly suitable for use in the non-destructive ultrasonic testing of tubes in the steam generators of pressurized water nuclear power stations (PWRs).
2. Prior Art
Testing devices are already known in which a head is provided with means for centering it in the tube and rendering an axis of the head coincident with or parallel to the axis of the tube; the head contains ultrasound transducer means coupled with the wall of the tube by immersion in a fluid, and is able to transmit an ultrasonic beam and to detect echoes due to longitudinally oriented defects.
As compared with eddy current testing devices, devices using ultrasounds have an apparent drawback: the echo delivered by a fault or flaw, such as a crack, varies greatly with the orientation of the fault. If for example an ultrasonic transducer is used delivering a beam directed along a meridian plane of the tube, it is difficult to detect longitudinal cracks and the longitudinal sections of long cracks having an intricate shape.